DEVELOPMENT. 217 



are, having a very close external resemblance. Barnacles 

 were long mistaken for Mollusks, Polyzoans for Polyps, 

 and Lamprey-eels for Worms. Such forms are termed 

 homomorphic. 



Members of one group often put on the outward ap- 

 pearance of allied species in the same locality : this is 

 called mimicry. " They appear like actors or masquerad- 

 ers dressed up and painted for amusement, or like swin- 

 dlers endeavoring to pass themselves off for well-known 

 and respectable members of society." Thus, certain Butter- 

 flies on the Amazons have such a strong odor that the Birds 

 let them alone ; and Butterflies of another family in the 

 same region have assumed for protection the same form and 

 color of wing, but lack the odor. So we have bee-like Moths, 

 beetle-like Crickets, wasp-like Flies, and ant-like Spiders : 

 harmless and venomous Snakes copying each other, and 

 Orioles departing from their usual gay coloring to imi 

 tate the plumage, flight, and voice of quite another style 

 of Birds. The species which are imitated are much more 

 abundant than those which mimic them. There is also a 

 general harmony between the colors of an animal and 

 those of its habitation. We have the white Polar Bear, 

 the sand-colored Camel, and the dusky Twilight -moths. 

 There are Birds and Reptiles so tinted and mottled as ex- 

 actly to match the rock, or ground, or bark of a tree they 

 frequent; and there are Insects rightly named "Walking- 

 sticks" and "Walking -leaves." These coincidences are 

 not always accidental, but often intentional on the part of 

 nature, for the benefit of the imitating species. Gener- 

 ally, they wear the livery of those they live on, or ape 

 the forms more favored than themselves. 



5. Homology, Analogy, and Correlation. 

 The tendency to repetition in the development of ani- 

 mals leads to some remarkable affinities. Parts or organs, 



